My car seems to have a cooling problem at idle. At stoplights, the water temperature doesn't hesitate to climb to 210-215, even on a mid-80's day. However, if I revv the engine to about 1200rpm while stopped, the temp quickly drops by about 15-20 degrees and stays there. My water pump pulley is 6.5", and the crank pulley is also 6.5" in diameter. I have a very mild engine making only about 280hp, original 4 core radiator, fan shroud and flex fan which is 1/2 way into the shroud. I changed the thermostat from 195 to 180 to 160 with hardly any change in temperature. Coolant/Water ratio is 50/50.

Is my problem a matter of getting a smaller water pump pulley or a bigger crank pulley, or is there something else you can think of? Thanks

If it's an automatic in gear your temp will be more prone to rise. If your sensor is on the left side head area it will read higher giving a more accurate view of head temps. Some have had problems with the newer orange antifreeze. There are so many variables in cooling from mechanical to igniton timing being more advanced. Idle speed and or an automatic trans getting hotter than normal. Do you have the correct shroud and number of cores radiator? My factory 4spd has an automatic radiator swapped in but at least it stay cooler. You should put a new radiator cap on every time changing fluid. If the caps too tight it can give problems. I think 18 is advised but I like 16lbs with the flip lever to release partial preasure. Good luck. I'd do a lengthy straight water hose flush with the main hoses disconnected at the radiator alternately plugging off lines to get a complete fill of chambers then dump with hose on full blast still inserted. Then once the water runs pretty clean pop the hoses on not tightening and run the engine with water filled to move sediment around then hose flush block and radiator again doing the plug and flush method. I like that for a first shot since if you'ld end up going the caustic chemical radiator flush method you wont be wasting chemicals on crud in the system.
Good luck. All of us old (hehehe more mature) guys have been there plenty of times and it's just another not again situation. I feel some type of flush is necesary. You have to start from a clean slate and the flush might be the cure.
Just looked at your website. Did the problem start after the shift kit?
Nice car and good luck.

The thermostat has NOTHING to do with operating temperature, nor does the radiator cap; the thermostat only determines MINIMUM operating temperature, and the cap only determines the point at which the coolant boils and "pukes" out through the overflow hose.

How is your vacuum advance connected? Ported or manifold vacuum? Makes a big difference in idle cooling - you want all the advance you can get at idle, and ported gives you only base timing. graemlins/thumbsup.gif

Snatchin', thanks for all of the info...Ill probably start with the cheapest of your recommendations first: the radiator flush. The radiator cap is some generic brand cap that came with the car, so ill check on its specs. Thanks a lot! Steven

JohnZ, I am actually not running vaccuum advance. However, I just printed out the instruction manual for my edelbrock carb, so I am going to give the idle screws a try, in case I am running too lean. Thanks though, I have found that many recommendations are better than too few.

I think this is a classic "air flow throught the core problem. Rev the engine a bit, the fan moves faster and moves more air through the core. This could be a timing issue as well though.

If you're already running 10 - 12 degs of initial advance I would suggest you drop the flex fan and replace it with a low dollar Flex-a-lite fan and thermal or non-thermal clutch (about $60 from Summit) and I bet your problem goes away.

One of the mags did a comparison test and next to electric or no fan at all the Flex-a-lite fans robbed the least power. I have had very good results keeping my 383 cool with the one I am using...

The caps change after a while for their release preasure even if you keep them clean. They can be used a long time but it's best to just change it when changing fluids. I don't advise the orange fluid. The brand I got has an orange cap also. Drove me nuts after I realised I was trying to double check my fresh flush looking at fluid that looked like rusty water. Some have posted other problems with it. Works good for me but I don't like the color.
If you just got the car, visually check the tubes of the radiator for having been pinched off to stop any leaks. Also the previous owner might of used a chemical plugger. Worse yet he might of been a submarine emergency repairman and popped pepper in the radiator to plug holes. It's true. It's been done.
I'm not sure how much a foriegn paint on the radiator to make it look newer would change the cooling but I'd figure it would have adverse effects.

sik try turning the idle screw up a tiny smidgin and see what happens. I would not worry about timing or mixture affecting the temp just yet. you seem to be on track with identifying the rpm helping. I would focus on coolant flow things like a collapsing rad hose or a simple pulley change. Having said that the temps you mention are really not that bad for a closed system. A Rad cap that maintains 12-16 psi pressure in your cooling system will keep everything under controll. those temps will help keep the plugs clean as well. Those are the temp ranges the GM engineers strive to maintain for peak efficiency and economy.

Good luck
Milan

I don't think a colapsed hose would open as the rpm increases. The over heating would continue when driving or raising the idle... Also just raising the idle isn't a resolution it's just a bandaid... Not knowing where the initial timing is at it's hard to say if more advance will help but I have seen 2 degs more initial settle idle temps of +200 deg to 180 many times. By bringing the idle up to 1200 rpm you have started the mechanical (and possible vacuum) advance increasing and that may be the reason the temp comes down. If it's not timing the fan is turning faster at 1200 rpm and pulling more air through the core dropping the fluid temp before it gets sent back to the block!!

About the only thing else I can think of is...
Radiator fluid. Make sure it's a proper blenb. One jug then water is too much for a 50/50 mix but It never bothers mine to run extra.
If the cap isn't allowing preasure release it's like a preasure cooker. You get extra temperatures compaired to design specs which is why I mentioned the cap ealier. The old design without overflow tank required having an inch or two of air space below the radiator cap to prevent over flow during the water expanding. If you dont have and over flow you might try leaving an air gap. Just rev the engine one time without the cap on and you'll take water out and be able to see if your pump is giving good water flow. I think that would be a good idea to check your water flow while you have the water drained out. At idle I think it's like 3-5 or so cores should be above the water line pumping water going to the bottom line directly below.
If the water pump is going you might be able to see some wobble. Plastic blades break and metal ones rust away so who knows.
And like DJD says, "I think this is a classic "air flow throught the core problem." You can have plenty of heat generating problems but with a good flow of air it's controlled.
If you have A/C running or an A/C evaporator in front of your radiator you have to expect a little more heat being retained.
Happy weekend.

I have to jump on this, Sik68. I would be willing to bet the change in my vehicle that its the flex fan your using. You may want to change to another brand that has wider blades. This whole thing happened to me. You have a 4 core w/ flex fan. I bought a wider blade from summit, OEM flex fan, last year. It had stiffer blades that move a considerable amount of air compared to the other style. Dropped the temp around 15 deg. Bingo! If you have added a clutch to it then that may be the problem as well. The clutch might no be operating at lower speeds. Try the Summit fan with the "stiffners", rather than the more flatter. Just my 2 cent!

Coolant level low????

Hehehe Sik68 I'm sitting here chuckling because a bunch of times I see guys posting looking to solve a problem and find out there are so many things that could cause a problem it's like you need an entire task force to work, document and analise the problem on the run. Good luck. Here's another. If you are running just water go 50/50 coolant and water or whatever is advised on the antifreeze chart on the jug.
Is your problem solved yet?

Commonly cooling down by reving the engine can be either the waterpump (low coolant flow) or the fan (if mechanical)(poor airflow) and sometimes a faulty thermostat (shuts at lower pressures).

I suggest use the new fangled tech fan from Derale heavy duty series. Part number 17XXX only...you will NOT be disappointed. Only $60 from Summit Racing. I hope you have a properly fitting shroud as well. This is important!

http://www.derale.com/img/ChromeHDFlexFan.jpg

Check out http://www.derale.com/flexfans.shtml for more information on size etc. This is the best mechanical fan going today. More air at idle and less at higher rpms. Simple as can be yet effective. Plan on using a spacer if you have a clutch.

Actually, for better heat transfer, the less antifreeze the better. You can run ethyl glycol (the green stuff) in partial percentages of only 25% and get BETTER heat transfer. Don't try this with the red stuff. The trick is getting rid of the extra heat at the radiator. Also, high flowing water pumps help with this too. I would consider this upgrade whereas stock pumps are dynosaurs compared with the newer high flowing ones.

Changing the thermostats to different opening/cycling points will not affect the cooling ability of a system one bit. Good change if you are suspecting the thermostat tho.

Check out my other cooling tips at http://www.inccn.net/techforum.htm for more ideas.

Whoa, I didn't know that checking back in this thread would give me so much more feedback! Thanks again to all, I think ill start with the cheap fixes, and gradually work my way up to a relatively expensive upgrade such as a different fan or water pump. Thanks graemlins/waving.gif

Also keep in mind that in order for a cooling system to work efficiently the water/coolant mix must spend a certain amount of time in the block, to absorb heat and then a certain amount of time in the rad to dissapate it. When I was a Moroso we were thinking of designing alum rads for all types of racing. What we found out is if the water curculates too fast through the engine and the rad the heat never gets dispersed. All you are doing is pumping hot water from one place to another. Heat dissapates from water through contact with the walls of the rad tubes. When the flow is too fast, a wall of super hot water becomes an insulator preventing the heat from being transfered. Best bet is to run a good thermostat, make sure that all the air is out of the system (find a shop that has an air-evac tool )run the proper pump pulley ratios and the proper mix. A bottle of water wetter never hurts either.

You know the "water moving too fast" deal was a pretty common thought until recently. Here's an opposing view:

Use a high performance water pump. These pumps move more water and provide higher pressure to help in the reduction of hot spots, reduce cavitation and take less horsepower to do such. Contrary to popular believe and long time myth, slowing the coolant through the radiator does not improve heat dissipation! I can’t emphasize this enough. This is a widely held myth that is completely contrary to the laws of heat conduction physics. The higher the flow, the more heat will get absorbed and dissipated. Stock water pumps are generally okay for stock engines, but are antiquated technology by today’s standards. The high performance pumps are a step up in cooling technology and reliability.

I took that from here:

http://www.inccn.net/jscooling.htm

Good info and gives another point of view.

Jody

Jody......you are exactly correct and well trained I might add in thermodynamic lessons. ;) Chassiboy comments mean well, but are confusing "laminar flow" with "flow" rate.

The physics facts are the more flow the higher the efficiency of the system in a closed loop system. The reason is simple. When water/coolant flow is reduced, slowed or sits in the radiator longer, the water also sits in the block longer. Water loses it's ability disproportionately to absorb and carry heat as it approaches it's corrected vapor point (boiling point at pressure N). What this means is that a unit of water at 170 degrees has a disproportionate capacity to absorb and carry more heat than let's say that very same unit at 200 degrees. As the water gets hotter more heat is left behind to build in the engine. The situation eventually gets to the point of overheating. And yes indeed this is the very principle that high flowing waterpumps are offered today to increase the capacity of the system. You just have to be able to dispose of the extra heat at the radiator to make the system effective.

Chassisboy mentioned moving water thru the radiator and "pushing hot water from one point to another". This is a laminar flow problem. What happens is just like in the summer when you jump in a lake and find that the surface water is warmed only to find the water at your feet or further down is cold. There is no turbulence or turnover in the water to warm the water evenly. This is laminar flow on a big scale and happens in a radiator environment also. Laminar flow can set up in your radiator and cause the water to flow thru your radiator with little mixing which leaves the middle of the stream still hot. This reduces the efficiency of the radiator. And lamilar flow tends to set up more in faster moving streams of water moving thru smooth sided tubed lengths. To alleviate this dimple tubes, baffles and directors are put in to introduce turbulence in the flow to make sure all of the molecules get bounced off the tubes to cool them so as to enhance (remember the lesson above on water heat absorbtion) their cooling capacity by lowering their temperatures. This is why you should never run without a thermostat because thermostats introduce turbulence to the incoming stream of water. :D

Very good information Jack and Jody. Its very similar to my in slab hot water heat in my garage. I can slow the flow or increase it with a valve (thermostat in the car comparable). If I speed the flow up too much, the heat pump compressor senses the water on return is to hot since it does not have time to release its heat completely on its run thru the slab and it shuts itself down, thinking the thermostat in the house has been satisfied. Its a delicate balance to get it just right, much like the right radiator, thermostat and hoses on a car. Great reading here folks.
graemlins/thumbsup.gif

Thanks for the correction and the detailed lesson. I thought those guys at Moroso were doing it wrong. I was the chassis engineer but often found myself involved in projects that had nothing to do with suspension! Give me a mig welder and some tube any day!

Originally posted by chassisboy:
Give me a mig welder and some tube any day! When can you start? :D

If you'll pay for relocation ....I'm there!!!!

Had the same problem with my '69. Nothing really worked until I replaced the stock water pump with a Stewart Perfomance one. Their high flow themostat is essential.
Not enough flow was my problem - since the temp sensor was in the head, the low flow allowed water to heat up quickly in the hottest part of the engine, as soon as engine (pump) speed came up the hot coolant was pushed from the head and the sensor was quick to respond to the cooler mixture. Had it been due to low air flow or a small/blocked radiator the temp guage wouldn't have responded so quickly to engine speed. It takes time to air cool 4 gallons of coolant.